Point of Reference Displacement and Motion Sensor

ABSTRACT

Sensors, devices, systems, devices, and methods for providing wireless modular self-contained units with battery power supply that can use radar, ultrasonic, and IR measuring techniques and sensors for directional detection of impeding objects, persons, or moving targets, and can be used with mobile smart phones and the like. The modular sensor units can be used as a displacement and motion measurement sensor for point of reference measurement applications. The displacement sensing method can use radar, ultrasonic, and IR measuring techniques for directional detection of impeding objects, persons, or moving targets. Upon the detection of the said target, algorithms make use of the direction, angle of ascent, and speed to provide real time position data represented in discrete format. The said sensors are modular in embodiment allowing for multiple sensors to be positioned in strategic regions on the person or system of interest to study the said frame using the method of moments to dissect the object in varying degrees of granularity. The sensor shall connect wirelessly to a mobile handheld (i.e. the end user&#39;s smartphone) device for real-time data acquisition along with seamless integration into an existing IMU only based system requiring information beyond six degrees of freedom as normally represented by gyros, and accelerometers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication Ser. No. 62/310,708 filed Mar. 19, 2016, the entiredisclosure of which is incorporated herein by specific referencethereto.

FIELD OF INVENTION

This invention relates to sensors, and in particular to sensors,devices, systems, devices, and methods for providing wireless modularself-contained units with battery power supply that can use radar,ultrasonic, and IR measuring techniques and sensors for directionaldetection of impeding objects, persons, or moving targets, and can beused with mobile smart phones and the like. Upon the detection of thesaid target, algorithms make use of the direction, angle of ascent, andspeed to provide real time position data represented in discrete format.Separate modular units each with multiple sensors to be positioned instrategic regions on the person or system of interest to study the saidframe using the method of moments to dissect the object in varyingdegrees of granularity. The wireless modular units can be used forreal-time data acquisition along with seamless integration into anexisting IMU (inertial measuring unit) only based system requiringinformation beyond six degrees of freedom as normally represented bygyros, and accelerometers. The IMU can include a sensor that measuresforces acting on a body in motion or at rest. In an automobile, an IMUwould measure acceleration of the vehicle which is useful in engagingthe cruise control system.

BACKGROUND AND PRIOR ART

Many types of sensors generally use either sonar or IR (infrared)sensors positioned off object and rely on the system in motion to traveltowards the sensor in a predetermined path of motion. Furthermore the 6degrees of freedom based systems are encumbered by the gravity vectorassociated with the accelerometers and require sophisticated filters toaddress such issues. The prior art sensors are also generally encumberedby drift which in turn can be quite inaccurate where precisiondisplacement information is needed as say in a physics classroomexperiment. Since these sensors require careful placement, the setup forsaid experiments can be more cumbersome than the experiment itself.

Thus, the need exists for solutions to the above problems with the priorart.

SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide sensors,devices, systems, devices, and methods using wireless modularself-contained units with battery power supply that can use IR(infra-red) and/or radar, and/or ultrasonic measuring techniques andsensors for directional detection of impeding objects, persons, ormoving targets, and can be used with mobile smart phones and the like.

A secondary objective of the present invention is to provide sensors,devices, systems, devices, and methods using wireless modularself-contained units with battery power supply that can use IR(infra-red) and/or radar, and/or ultrasonic measuring techniques andsensors, where upon the detection of the said target, algorithms makeuse of the direction, angle of ascent, and speed to provide real timeposition data represented in discrete format.

A third objective of the present invention is to provide sensors,devices, systems, devices, and methods using wireless modularself-contained units with battery power supply that can use IR(infra-red) and/or radar, and/or ultrasonic measuring techniques andsensors, where separate modular units each with multiple sensors to bepositioned in strategic regions on the person or system of interest tostudy the said frame using the method of moments to dissect the objectin varying degrees of granularity.

A fourth objective of the present invention is to provide sensors,devices, systems, devices, and methods using wireless modularself-contained units with battery power supply that can use IR(infra-red) and/or radar, and/or ultrasonic measuring techniques andsensors, where the wireless modular units can be used for real-time dataacquisition along with seamless integration into an existing IMU onlybased system requiring information beyond six degrees of freedom asnormally represented by gyros, and accelerometers.

A fifth objective of the present invention is to provide sensors,devices, systems, devices, and methods using wireless modularself-contained units with battery power supply that can use IR(infra-red) and/or radar, and/or ultrasonic measuring techniques andsensors, to allow the physics students or researcher the opportunity todeduce motion from both the integrals of acceleration, and thederivative of displacement vectors. In doing so we are providing thefirst sensor to allow for both features in a single unit.

The detection mechanism can also include Doppler information from aradar with a highly directional antenna or time-of-flight using an IRtransmitter and receiver along with ultrasonic waves in certainembodiments. The sensors are collocated in an electronic assembly thatcan be affixed to the device-in-motion's frame of reference with theradar/light transceiver pointed along the axis of advancement. Thesensor will contain said displacement mechanisms on each axis x, y, zand for 3 degrees of freedom displacement wise. The onboardaccelerometer shall be used to resolve angle when motion becomes offaxis. The sensor will be passive with regard to the body in motionmeaning it shall not need to be tethered by physical wire to the datacollection device.

The circuit card assembly that houses the printed wiring board (PWB) isphysically dimensioned to be worn with comfort in an e-garment. The PWBshall contain all electronics for conversion of the radar and IRsensors, along with an inertial measurement sensor data for wirelesstransmission to the host person's mobile device. The circuit cardassembly will combine the PWB, a coin/lipo battery, low-power processor,and piezo-vibrators.

The system is designed to maximize battery life by placing the sensorsin a low-power mode until target excitations exceed a threshold inventon the sensor. Upon excitation, the sensor shall begin collecting dataanalyzing targets coming within proximity of the sensor. The softwareshall place the sensor back in the sleep mode when excitations ceaseover a specified time interval.

The wireless link shall support the Zigbee, Bluetooth, and ANT+communication protocol. The chosen antenna and RF (radio frequency)substrate are fully compatible with all competing lower-powerstandards/communication radios.

The sensor software suite running on the host mobile device shallcompute the sensor data for analysis per the desired outputs asspecified by the end user.

The novel sensor unit can be housed in a portable housing having agenerally disc shape with a front side having a raised uppersemi-circular portion, and a lower recessed semi-circular portion, and agenerally flat rear surface. The sensor unit can be fit into a novelholster having a narrow rectangular cavity for allowing the recessedsemi-circular lower portion of the front of the sensor unit to beslipped inside. The holster can have upwardly protruding curved legswhich can wrap about the curved sides of the generally disc shapedhousing of the sensor unit.

Further objects and advantages of this invention will be apparent fromthe following detailed description of the presently preferredembodiments which are illustrated schematically in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the quadrature and phase transceiver circuitry used in amodular unit that exploits the time-of-flight of as in IR orelectromagnetic waves in reference to a target.

FIG. 2 shows an embodiment of the modular sensor unit observing motionfrom the point of reference of spring mass system in a classroom typeexperiment.

FIG. 3 shows another embodiment of using multiple modular sensor unitslocated at different location points in front of a 2D (two dimensional)camera.

FIG. 4 shows a battery operated modular sensor unit spaced apart and inwireless communication with a mobile computing device, such as a smartphone.

FIG. 5A is an upper left front view of the modular sensor unitreferenced in the previous figures.

FIG. 5B is an upper right front view of the modular sensor unit of FIG.5A.

FIG. 5C is a rear view of the modular sensor unit of FIG. 5A.

FIG. 6A shows a screen shot of the motion displacement sensor data thatcan appear on a computer, smart phone, and the like.

FIG. 6B and 6C show graphs of application data for a user to downloadand record in a physics notebook.

FIG. 7A shows a sensor in an embodiment on a track measuring motion dataon a track.

FIG. 7B is an exploded view of the sensor unit and holster shown in FIG.7A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before explaining the disclosed embodiments of the present invention indetail it is to be understood that the invention is not limited in itsapplications to the details of the particular arrangements shown sincethe invention is capable of other embodiments. Also, the terminologyused herein is for the purpose of description and not of limitation.

In the Summary above and in the Detailed Description of PreferredEmbodiments and in the accompanying drawings, reference is made toparticular features (including method steps) of the invention. It is tobe understood that the disclosure of the invention in this specificationdoes not include all possible combinations of such particular features.For example, where a particular feature is disclosed in the context of aparticular aspect or embodiment of the invention, that feature can alsobe used, to the extent possible, in combination with and/or in thecontext of other particular aspects and embodiments of the invention,and in the invention generally.

In this section, some embodiments of the invention will be describedmore fully with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will convey the scope of the invention to those skilled inthe art. Like numbers refer to like elements throughout, and primenotation is used to indicate similar elements in alternativeembodiments.

A list of components will now be described.

1 modular self-contained sensor unit

10 microprocessor

20 IMU 60F inertial measurement unit with six degrees of freedom,

30 RF (radio frequency) synthesizer emits discrete sinewave tones. Theincident wave is transmitted as electromagnetic waves that is bothabsorbed and reflected off of the target. The reflected waves areexploited for magnitude and phase.

35 refers to a circulator used as a reference signal

40 flash memory is an on board non-volatile memory that storescalibration and other user definable data that survives powering thedevice on/off.

50 refers to a quantizer (an analog to digital converter)

60 Radiating Element (antenna)

70 photo detector for transporting the electromagnetic waves throughfree space air.

75 IR (infrared) transceiver transmits and receives sinewaves asphotonic light energy, with IR demodulator

80 antenna for electromagnetic waves

85 RF demodulator

100 transmitted and received echo waveform

110 target can be any surface that that beams come into contact with

200 spring mass system

210 mass

220 spring

230 anchor reference point

240 displacement

250 modular sensor unit

260 time of flight

270 surface

300 person to Person Situational Awareness Embodiment of a joggingperson

310 sensor unit module

320 sensor unit module

330 sensor unit module

340 2D camera

345 mount surface

400 modular sensor unit and smart phone embodiment

405 circuit board

410 receiving information bandwidth

420 coin cell battery

430 chip antenna

440 smart phone

500 modular sensor unit housing

510 front side

512 Upper raised portion

514 stepped area

515 field of view

516 recessed bevel

520 IR indicator

530 charging port

540 on/off button

550 IR transmitter (one of the optical components)

560 IR photodetector (another one of the optical components)

570 rear side

575 fasteners, such as screws, bolts, and the like.

590 flat surface

580 battery indicator

600 screen shot

605 recorded displacement data

610 email

615 velocity graph

617 accelerometer data

700 track motion embodiment

710 sensor

720 moving cart

730 holster

732 left side curved leg

735 inside cavity of holster 730

738 right side curved leg

750 track

FIG. 1 shows the quadrature and phase transceiver circuitry used in amodular unit 1 that exploits the time-of-flight of as in IR orelectromagnetic waves in reference to a target 110. A general purposemicroprocessor 10 can be used which is capable of performing essentialDSP (digital signal processor) functions as related to time andfrequency domain frequency processing.

The IMU (inertial measuring unit) 60F 20 can include but is not limitedto an IMU used in U.S. Pat. No. 4,589,610 to Schmidt, which isincorporated by reference in its' entirety. U.S. Pat. No. 4,589,610 toSchmidt describes an example of using an IMU to deduce motion in aguidance system. The subject invention is taking this IMU informationand reporting it to the end user through an app so that children canlearn about the motion of objects in free space. In order to getposition data, Kalman filters can be applied and in doing so these arehigh quality estimates. We are adding the displacement sensor into themix so that the missile or toy knows it's absolute range to a target.

Other types of sensors can be used such as but not limited to radar andultrasonic transducers, piezo-vibrators. and the like.

Referring to FIG. 1, the modular sensor unit 1 can be used fortransmitting and receiving an echo waveform 110 off of a moving orstationary target 110. The sensor unit 1 combines a transceiver unitthat emits and receives a radiated pulse as reflected from the target110. The synthesizer 30 is responsible for producing discrete tones. Theradiating element 60 can be an antenna for electromagnetic energy or anIR emitter of an optical system. In either case the transmitted signalis quantized 50 as the reference signal 35 to the time-of-flight 100processing engine.

The received signal is processed using an antenna 80 for theelectromagnetic wave where the received signal is demodulated using anRF demodulator 85. The received signal is processed using photodetector70 for the photonic wave where the received signal is demodulated usingan IR demodulator 75. This phase delta 100 is used to compute thedistance to the target in the digital signal processing unit on themicroprocessor 10. The inertial measurement data 20 (i.e. acceleration,and angular acceleration data) are combined in a vector form and storedon the on-board flash memory 40.

Three axis of acceleration, and three axes of angular accelerationresults in six degrees of freedom (6OF). The processed sensor data isboth stored on the flash 40 and transmitted in real time using apersonal area network which can include Bluetooth, Wi-Fi, and otherradio protocols providing truly untethered telemetry data.

FIG. 2 shows an embodiment 200 of the modular sensor unit 250 observingmotion from the point of reference of spring mass system in a classroomexperiment. In the analysis of a spring mass system 200 affixed to areference point 230 the sensor unit 250 can be attached to the mass 210at the end of the spring 220. As the mass oscillates up and down due tothe pull of gravity, the displacement 240 from floor 270 increases anddecreases respectively. The sensor unit 250 measures this distance usingthe waves 260 transmitted and reflected from the floor 270 and at thesame time records and stores the linear and angular acceleration datafor the user observing the experiment.

FIG. 3 shows another embodiment of for a person to person situationalAwareness application 300 of using multiple modular sensor units 310,320, 330, and more located at different location points of a moving bodyin front of a 2D (two dimensional) camera 340 on a support mount surface345.

Take the case of an athlete 300 shadow performing in front of a wall345. In some cases, a 2-D camera 340 can be mounted as a secondary aidin training for performance and power by monitoring technique. Multiplesensors 310, 320, and 330 can be placed at key places of motion alongthe body 300 can relay said information back to a host mobile device(FIG. 4) to combine the sensor data into a personal area network.

A personal area network (PAN) is the interconnection of informationtechnology devices within the range of an individual person, typicallywithin a range of 10 meters. Transmitting data wireless over a shortdistance. Bluetooth and Wi-Fi Direct are examples of personal areanetworks (PANs).

The distance of each sensor 310, 320, and 330 as measured with respectto the wall 345 can be combined to analyze a sprinter's running motionon a treadmill by correlating the runners arm stride 310 with their quadexplosion 320 to determine if they are overcompensating for weak lowerleg muscles 330.

The sensor units 310, 320, 330 can provide depth from the camera 340 tomake for three-dimensional data points for motion tracking of theindividual points on the subject of interest. The information can beused for tracking during animation to provide ultra-realistic modelingof the person in a computer animation.

FIG. 4 shows an embodiment 400 of battery operated modular sensor unit(such as the previously shown and described sensor units) spaced apartand in wireless communication with a mobile computing device 440, suchas a smart phone, portable computer, and the like.

The electronic circuit assembly 400 part of sensor unit 1 is responsiblefor housing circuit board 405 along with chip antenna 430 fortransmitting and receiving information 410 from the smart phone ormobile computing device 440. The said unit is low energy device capableof running for extended periods of time off of a single coin cell 420.

The sensor unit 400 is not a throw-away device upon depletion of thecoin-cell battery 420. The chip antenna 430 can be low profile in designand collocated with the rest of sensor electronics using an RF (radiofrequency) substrate on the top side of the PWB.

The advantage of such design is that there are no additional mechanismsto connect to the bicycle that might suffer damage due the normal rigorsof an e-garment. The bandwidth 410 of the chip antenna 430 iscommensurate with the low-power radio already utilized in industrystandard smartphones, so the smartphone 440 does not require any specialadapters to communicate.

FIG. 5A is an upper left front view of the modular sensor unit 500 in amechanical housing having a generally disc shape up to approximately afew to several inches in both diameter and thickness, which can housethe components that were referenced in the previous figures. FIG. 5A isa front side of the modular unit 500. The mechanical enclosure 500 forthe sensor unit 1 FIG. 1) is responsible for housing circuit board 405(FIG. 4) along with the sensor optics, previously described. The fieldof view 515 is determined by the spacing between the optical elements550, 560 positioned behind a pair of circular openings in the front ofthe housing, and is intentionally tight for a direct and long extendingbeam. This both increases range and sensitivity of the sensor distance.

Under an outwardly extending upper portion 512 there stepped area 514leading to a recessed bevel 516 for mounting the sensor unit 500 in amotion cart enclosure 730 shown and described in relation to FIGS.7A-7B. The IR indicator 520 alerts the user with a visible lightemission as to when the unit 500 is transmitting IR pulses to calculaterange.

FIG. 5B is an upper right front view of the modular sensor unit 500 ofFIG. 5A. The sensor unit 500 contains a charging port 530 which acceptsa standard USB cable. The on/off button 540 is recessed to notinadvertently power the sensor off while concealed in an object thatmight absorb shock (i.e. nerf football). The IR transmitter 550 emits anIR pulse that is detected by the IR photodetector 560 which contains afilter to lessen sensitivity to ambient light again improving sensorrange.

FIG. 5C is a rear view of the front view of the modular sensor unit 500of FIG. 5A. Other than the mechanical fasteners 575 the sensor is flat590 so that it may be adhered to objects with any mounting technique,such as but not limited to peel and stick tape, hook and loop fasteners,other adhesives, and the like. There are two indicators 580 to indicatewhen the sensor has completed charging and when in use, if the batteryis critically low. For example, a solid color, such as green canindicate the unit is being charged, and a flashing red color canindicate the unit is running low on battery life.

The sensor unit 500 can be used to corroborate inertial measurement datawith the displacement information for 7 degrees of freedom in motionanalysis. The sensor unit 500 can be modular for user specific regionsof motion observation for a combinatorial motion map of said targets ofinterest.

The sensor unit 500 reports said information in multiple data outputsfor digital realization using smart devices and other mobile computingplatforms.

The wireless modular sensor units 500 can be used for real-time dataacquisition along with seamless integration into an existing IMU onlybased system requiring information beyond six degrees of freedom asnormally represented by gyros, and accelerometers.

The sensor units 500 used in the novel system are designed to maximizebattery life by placing the sensors in a low-power mode until targetexcitations exceed a threshold invent on the sensor. Upon excitation,the sensor shall begin collecting data analyzing targets coming withinproximity of the sensor. The software shall place the sensor back in thesleep mode when excitations cease over a specified time interval.

The wireless link shall support the Wi-Fi, Zigbee, Bluetooth, and ANT+communication protocol. The chosen antenna and RF (radio frequency)substrate are fully compatible with all competing lower-powerstandards/communication radios.

The sensor unit 500 can use software running on the host mobile deviceshall compute the sensor data for analysis per the desired outputs asspecified by the end user to include useful information in physics labexperiments like displacement graphs, acceleration graphs, and rangeplots etc.

FIG. 6A shows a screen shot 600 of motion displacement sensor data thatcan be displayed on portable computers, smartphones, and the like. Therecorded displacement data 605 gathered by the sensor in real-time canbe e-mailed 610 to the end-user or stored on the cloud in networkedclassrooms. If the user chooses they can simply observe live motion byholding the sensor in their hands or setting off an experiment whilevisually watching the displacement data. FIG. 6B shows a graph 610B ofx-Axis Position data shown in the screen shot 600 of FIG. 6A.

FIG. 6C is a graph 610C of x-Axis Velocity data that can also come fromthe screen shot 600 of FIG. 6A. By taking the derivative of thedisplacement data the physics student can trace the velocity graph 615along the objects path of motion. This is a derived plot from thedisplacement data recorded by the sensor. It should also be noted thatthe on-board accelerometers are also recording motion. The physicsstudents can produce this same graph with the integral of theaccelerometer data 617. They will note a cleaner profile without the aidof the filters on the displacement plots because it doesn't suffer theeffects of the gravity vector. No other physics sensor provides bothacceleration and displacement in a single unit.

FIG. 7A shows an embodiment 700 of using the novel sensor unit 500mounted in a holster 730. The motion of a cart down a track is onepopular physics experiment 700. The cart 720 is allowed to acceleratedown the track 750. Most competing systems use an ultrasonic sensor atthe end of the track to record the displacement. With our system, werecord the motion from the perspective of the cart 720 as it acceleratesdown the track. The sensor 500 is affixed to our motion cart using ourdedicated holster 730 which is designed to both absorb vibration and tonot block the radiating element 550 and the receiving element 560 duringthe motion down the track 750.

FIG. 7B is an exploded view of the novel modular sensor unit 500 removedfrom the mounting holster 730. To start an experiment, the pliable andbendable curved legs 732, 738 can bend outward as the unit 500 is pusheddown into the holster 730, and snap back to wrap about the curved sidesof the sensor unit 500 as the recessed bevel portion 516 of the unit 500is sized so as to slip into the cavity portion 735 of the holster. Whenthe experiment is done the sensor 500 can be popped out from the holster730 and ready for use in a different experiment. The novel holster canbe used to mount the sensor unit 500 to any surface. The underside ofthe novel holster 500 can be adhered to any surface by various types offastening techniques that can include but are not limited to hook andloop fasteners, peel and stick tape, and any other types of fasteners,and the like.

The term “approximately” can be +/−10% of the amount referenced.Additionally, preferred amounts and ranges can include the amounts andranges referenced without the prefix of being approximately.

While the invention has been described, disclosed, illustrated and shownin various terms of certain embodiments or modifications which it haspresumed in practice, the scope of the invention is not intended to be,nor should it be deemed to be, limited thereby and such othermodifications or embodiments as may be suggested by the teachings hereinare particularly reserved especially as they fall within the breadth andscope of the claims here appended.

I claim:
 1. A point of reference displacement and motion sensor modulecomprising: a portable housing; a motion and displacement sensor insidethe portable housing; a wireless transmitter inside the housing; and abattery power supply inside the housing, wherein the motion anddisplacement sensor senses information from a target to transmit in awireless communication to a remote location.
 2. The point of referencedisplacement sensor module of claim 1, wherein the motion anddisplacement sensor includes: an electromagnetic/radar transceiver andreceiver inside the housing; or an infrared transceiver and receiverinside the housing.
 3. The point of reference displacement sensor moduleof claim 3, wherein the radar transceiver and receiver includes; atleast one of radar, ultrasonic and Doppler radar.
 4. The point ofreference displacement sensor module of claim 1, wherein the batterypower supply includes: a coin cell battery.
 5. The point of referencedisplacement sensor module of claim 1, further comprising incombination: a smart phone spaced apart from the sensor module forreceiving data from the sensor module.
 6. The point of referencedisplacement sensor module of claim 1, wherein the motion anddisplacement sensor includes sensors of measuring speed and directionfrom the target.
 7. The point of reference displacement sensor module ofclaim 1, wherein the motion and displacement sensor corroboratesinertial measurement data with displacement information for 7 degrees offreedom in motion analysis.
 8. The point of reference displacementsensor module of claim 1, wherein the motion and displacement sensorincludes: sensors for mapping motion of the target.
 9. The point ofreference displacement sensor module of claim 1, wherein the portablehousing includes: a generally disc shape.
 10. The point of referencedisplacement sensor module of claim 9, wherein the portable housingincludes: a front side having an upper raised generally semi-circularsurface; and a lower stepped in recessed semi-circular surface.
 11. Thepoint of reference displacement sensor module of claim 10, wherein theportable housing includes: a rear side with a generally flat circularsurface.
 12. The point of reference displacement sensor module of claim11, further comprising: a holster with a cavity for allowing the lowerstepped in recessed semi-circular surface portion to be insertedtherein.
 13. The point of reference displacement sensor module of claim12, wherein the holster includes: a pair of upwardly protruding curvedlegs for wrapping about sides of the portable housing, when the lowerstepped in recessed semi-circular surface portion of the housing isinserted into the cavity of the holster.
 14. The point of referencedisplacement sensor module of claim 10, wherein the portable housingincludes: a pair of portals spaced apart from one another on a frontsurface of the generally disc shape portable housing.
 15. The point ofreference displacement sensor module of claim 14, wherein the pair ofportals includes: an IR transmitter which emits an IR pulse that isdetected by an IR photodetector which contains a filter to lessensensitivity to ambient light for improving sensor range.
 16. The pointof reference displacement sensor module of claim 8, wherein thegenerally disc shape portable housing include: a recessed charging port530 for accepting a USB cable to allow for the battery power supply tobe recharged.
 17. The point of reference displacement sensor module ofclaim 8, wherein the generally disc shape portable housing include: arecessed on and off button switch for turning the sensor module on andoff, the on and off button switch being recessed so as to notinadvertently power the sensor off while concealed in an object thatmight absorb shock.